If the total length of diagonals of a cube is 12 cm, then what is the total length of the edges of the cube ?

Answer: Option D

Since a cube has 4 diagonals, we have :
Length of a diagonal
$$\begin{array}{rl}& =\left(\frac{12}{4}\right)cm\\ & =3cm\end{array}$$
Let the length of each edge of the cube be a cm
Then,
$$\begin{array}{rl}& \sqrt{3}a=3\\ & or,a=\sqrt{3}\end{array}$$
∴ Total length of the edges of the cube = $$12\sqrt{3}$$ cm